Method of making porous metal objects



Patented Oct. 18, 1938 UNITED STATES PATENT QFFICE Chester Tietig, Covington, Ky.

N 0 Drawing.

8 Claims.

This application is a refile in part of my former application Serial No. 720,814, filed April 16, 1934 entitled Porous metal objects and method of-making same, which wasallowed July 15, 1936. The present invention relates to method of making porous metal objects such as bushings, bearings, bullets and lubricating buttons used in automobile springs.

One of the objects of the invention is to produce a more porous object of this class, i. e., one which will absorb more oil.

Another object is to make such articles which are stronger than those made commercially at present and which have better qualities both as to strength and lubricating qualities and those used at present as bearings or bullets. The invention comprises the articles as well as the method of manufacture.

Briefly stated, the principle upon which the invention rests is that a metal oxide particle, when incorporated with a body made up of powdered elemental metal, which is pressed and the oxide then reduced chemically at high temperatures, will leave large numbers of small voids due to the abstraction of oxygen from the oxide, if care be used to merely sinter but not to melt the resulting metal.

My method of procedure is to take finely divided metal powders such, as are customarily used to make the objects mentioned and to mix with them from 2% to 20% by weight of an easily reducible oxide of one or more of such metals, i. e., copper oxide, tin oxide, zinc oxide, or cadmium oxide. I then press the mixture into the desired shape under heavy pressure and then reduce the oxide in a furnace with reducing temperature not exceeding 1700" F. that is not exceeding the fusing point of any of the materials present to the extent that the desired voids would be filled up by the fusion of any component. The latter point, of course, varies according to the composition employed. Up to 6% the weight of finely divided graphite may be employed in such mixtures.

Illustrating my invention by way of example, and using the preferred oxide, CuO, I press the powdered material at from 12,000 to 25,000 pounds per square inch. Even higher pressures may be employed, but they are not necessary. The compositions are, in per cent by weight:

Copper Tin Zinc 32% igg Graphite The original materials are in the form of powder which will pass a standard 200 mesh screen.

Application August 30, 1937,. Serial No. 161,589

The pressed objects are sintered in furnace with a reducing atmosphere which is preferably hydrogen, or city gas, the latter either natural or artificial. The sintering of the above composition is done at from 1200 to 1400 Fffor from 1 to 3 hours. The products are then cooled under non-oxidizing conditions and then impregnated with lubricating oil before use. They are preferably machined when close fits are necessary as in the ease of hollow cylinders to be used as bearings. The machining is done either before or after the oil impregnation.

Bushings made of the-above materials by the process of manufacture given, will absorb from 10% to 45% of their own volume of oil. The beneficial influence of copper oxide is shown by the fact that bushing of the last composition given (10% CuO) will absorb 45% more oil by weight than those having only 3% CuO content.

The final step of manufacture i. e. the impregnation with lubricating oil is accomplished by immersing them in the oil or melted grease in a covered vessel and exhausting the air from above the oil. The vacuum should be held for several hours for maximum results and better impregnation is obtained if the oil is kept hot, but below its boiling point. The grade of oil selected will of course be governed by the duty to which the object is to be subjected. For heavy work at high temperatures a heavier oil will be more desirable than a thin oil. A heavy oil can also be more successfully introduced if slightly thinned with a light solvent such as gasoline. In such treatment the vacuum may be reduced or dispensed with entirely.

In use the objects described cause to exude oil when subjected to heat or to friction. In bullets made according to the invention much higher velocity may be had with the same powder charge than with a dry bullet coupled with less wear upon the bore of the firearm. In bullet manufacture a lead oxide such as litharge, red lead or white lead may be used in place of the copper oxide, tin oxide or zinc oxide. However, for high velocity bullets I prefer those made with the latter oxides especially with copper oxide. For bullets intended for extreme velocities a higher forming pressure than 25,000 pounds may be used.

Objects, especially bearings may also be made according to the invention of powdered silver and powdered cadmium oxide and/or the components to give the ratios of components present in the connecting rod bearings used in certain makes of automobiles, notably Ford. In making these cadmium oxide is reduced in the presence of the powdered silver to make a unitary structure containing a large number of pores, which are then impregnated as usual.

If desired, impregnation with lubricant can be dispensed with in many cases, and the objects used unlubricated or merely lubricated without being vacuum impregnated.

In this specification and claims city gas means either natural gas or gas powdered from coal or coke.

An essential of the invention is that only sintering and not definite fusion should be produced. Expert metallurgists will know how to produce the desired result by my method and to vary their temperatures and treatment times for various compositions so as to avoid closing the pores.

I claim as my invention:

1. The process of making porous metal objects which comprises mixing finely divided dissimilar metal powders with an easily reducible metal oxide, then forming the object under high pressure and then reducing with a reducing gas substantially the entire amount of the oxide to create voids while preserving the general shape of the object and substantially avoiding alloying.

2. The process of making porous metal objects which comprises mixing dissimilar finely divided metal powders and a non-metallic solid lubricant with an easily reducible metal oxide, forming the object under high pressure and then reducing substantially all of the oxide with reducing gas while preserving the general shape of the object and substantially avoiding alloying.

3. The process of making a porous metal object which comprises mixing dissimilar finely divided metal powders with a minor proportion of an easily reducible metal oxide, forming the object under high pressure, reducing all of the metal oxide to metal with a reducing gas without substantially altering the general shape of the object and substantially avoiding alloying and then impregnating the porous object with oil.

a. The process of making a porous metal object which comprises mixing finely divided powders of elemental common bearing metals with graphite and a minor proportion of an easily reduced metal oxide, pressing the objects to shape at a minimum of 12,000 lbs. per sq. inch, reducing substantially all of the oxide and sintering the powder at an elevated temperature in a. reducing gas while preserving its general shape and substantially avoiding alloying and then impregnating the porous object with oil.

5. The process of making a porous metal object of good anti-friction qualities which comprises mixing dissimilar elemental powders of at least 200 mesh fineness, selected from the group comprising copper, zinc, tin and aluminum with a minor proportion of an oxide selected from the group zinc, copper and tin, heavily pressing it into an object, reducing substantially all of the oxide and sintering the powder in a reducing gas without materially altering the general shape of the object or alloying the metals and then impregnating the object with oil.

6. The process of making a porous metal object of good anti-friction qualities which comprises mixing two or more dissimilar elemental metal powders selected from the group copper, zinc, tin and aluminum, all of 200 mesh or finer, with a minor proportion of a finely divided metal oxide selected from the group comprising copper oxide, zinc oxide and tin oxide, pressing the resulting mass into an object at a pressure ranging from 12,000 lbs. to 24,000 lbs. per square inch, sintering the object While substantially avoiding the alloying thereof and reducing substantially all of the oxide in a gaseous reducing atmosphere at a temperature between 1200 F. to l700 F. and then impregnating the resulting porous object with oil.

7. The process of making a porous metal object of good anti-friction qualitieswhich comprises mixing by weight, from 74% to 94% of copper powder, 7.2% to 10% of tin powder, 2% to 18% of zinc powder, 2% to 20% of an oxide selected from the group copper oxide, tin oxide, and zinc oxide and from a trace to 6% graphite, all in finely divided condition, pressing the resulting mass at from 12,000 to 24,000 lbs. per sq. inch, and then heating the objects so formed while preserving their general shape for from one to "three hours in a reducing atmosphere prepared from the gases of the group hydrogen, natural gas, artificial city gas made from coal.

8. The process of making a porous metal object of good anti-friction qualities which comprises mixing by weight from 82% to 86% of copper powder, a trace to 10% of zinc powder, a trace to 1.2% of aluminum powder, a trace to 3.0% of graphite and 3% to 10% of copper oxide, all in very finely divided condition, pressing the resulting mixture into the form of objects at a pressure of from 12,000 to 24,000 lbs. per sq. inch. and then heating the so formed objects from one to three hours in an atmosphere of hydrogen while preserving their general shape and then impregnating the said objects with lubricating oil.

CHESTER TIETIG.

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